Problems with 12 V and 110 in Same Conduit?

[GrundgeDog]

So I'm guessing...... No then?
Just kiding, I will make separate lines of conduit!! Especially because I am not good at putting the smoke back in electronics once it comes out !!!

[Larwyn]

Wow! I've just gotta post on this one! I swore off the electrical posts; there are so many expert opinions. But this one I can't resist.

Wires can rub together and insulation wear away whether they carry 110VAC or 12VCD. This is a good reason to run you 110V hot line in a separate conduit from the neutral. And add a third conduit for ground. Plus one for the 12Vplus and and a separate Ground. If you work it right, you can put so much conduit in this trailer you won't need walls!

OK, I apologize for being annoying. My solution was to use good stranded wire with really tough insulation. Ran it wherever I wanted, sometimes 12VDC right next to 110VAC -- and no conduit for any of it. I have fuses and breakers and I will take the chance of blowing out something when the 12V shorts to the 110V, if that ever happens. There are no doubt other solutions just as good; perhaps some better. Mine's good enough for me.

I could not agree more.

But something I think that you and I both fail to take into consideration is that the subject here involves teardrop electricity. Teardrop Electricity whether AC or DC, it seems, is much more flammable and deadly than the power plant/transmission line/control circuit electricity that I worked with for so many years. There is even danger if you do not separate the chassis DC from the house DC circuits. And do not forget that very strict National Home Built Teardrop Electrical Code which, I believe, is a thinly disguised Federal Law designed to make felons of us all.

It is quite possible that Teardrop Electricity is so dangerous that consideration of alternatives might be warranted. You can find lights that are powered by dry cell batteries, which though in fact, are DC powered eliminate all those dangerous external wires. DO NOT under any circumstances be taken in by those extremely dangerous rechargeable devices, as they foolishly have you inject AC voltage into a box box full of DC to shock those batteries back to life. If there is a box on the end of the charging cord, then you need to be certain there are no AC power cords near the wire going to the device being charged as it is carrying DC voltage. If it is a simple AC power cord is used for charging, you have the most dangerous situation of all as you now have both AC and DC in the same, usually plastic, housing along with all the other circuitry inside.

Unless you are a highly trained electrical engineer with absolutely no technical, hands on experience, you should probably never consider wiring anything on a TD. I would even advise calling in an expert if you find that someone has foolishly unplugged the connector between the TD and the tow vehicle. Even though this plug can only be connected one way, you are better safe than sorry. Remember both TDAC and TDDC are much more deadly than simple AC or DC voltage.

Sorry, that wannabefree fella made me do it........

[Miriam C.]

Yes some of us get careful. And some get way outta hand. However it hurts nothing and I personally see no reason to run TD12VDC ina conduit.

[BobU]

Sounds like these postings worry about the wires "rubbing thru" That is the reason that we all have properly sized fuses and/or breakers. As far as running different votages in the same conduit, That shouldn't cause a problem as long as the wire insulation is rated for the higher voltage. By using a color coding system, to keep track of one voltage from the other, we shoold be able to keep all the smoke in the electronics where it belongs.

[caseydog]

I guess the point I'm trying to make is that we all make mistakes. Now, if you make a plumbing mistake, you can get things wet. If you make an electrical mistake, you might just ruin a light bulb, or you might start a fire, or you might electrocute yourself or someone you care about.

Soooo, with the potential cost of a mistake that high, why not go out of your way to keep things as safe as you possibly can?

If I were going to mix low-voltage DC and 100V-AC in one camper, I would put as much separation as possible into the two systems.

CD

[planovet]

I would even advise calling in an expert if you find that someone has foolishly unplugged the connector between the TD and the tow vehicle. Even though this plug can only be connected one way, you are better safe than sorry.

Sounds like a union man to me. Of course you would need at least 2 engineers to do it, one to supervise and one to do the work.

[Larwyn]

No union here, just poking a little fun at some of the advise I've seen on the electrical forum.

If it were union. It would take the engineer to check the design, a laborer to lift the plug off the ground and an electrician to make the connection. I worked as a consultant in a couple of union states. As non union I was not allowed to do anything other than tell the representative of the proper trade to do what I would have done on my own in Texas. Hope to never have my hands tied like that again!!!

[Larwyn]

I guess the point I'm trying to make is that we all make mistakes. Now, if you make a plumbing mistake, you can get things wet. If you make an electrical mistake, you might just ruin a light bulb, or you might start a fire, or you might electrocute yourself or someone you care about.

Soooo, with the potential cost of a mistake that high, why not go out of your way to keep things as safe as you possibly can?

If I were going to mix low-voltage DC and 100V-AC in one camper, I would put as much separation as possible into the two systems.

CD

Drowning ever crossed your mind??? A person can drown in very shallow water, so if you are not sure of those connections, think twice before hooking up to that campground tap..........

[wannabefree]

Well, I just cut out some of my best browbeating to get to the bottom line. Some of you should thank me for that this is long enough already and I worked hard not to be offensive.

We engineers engage regularly in an exercise called risk management. We all do it, structural, electrical, civil, aerospace -- every engineer. You can't get away from it. It's easy:
1) identify a risk and what bad will come from it.
2) Then postulate (um, that's guess, my friend -- engineers guess, all the time. Scary...) ways the risk can be mitigated (erased).
3) Figure out the cost of the mitigation.
4) figure out how probable it is the nasty event will occur -- that's usually a guess, too.
5) based on the probability of the risk occuring, decide if it's worth the cost of mitigating the risk.

Now in this case, the risk is that a 110V wire and a 12V wire will wear away their insulation in exactly the same place and short together, causing the trailer to spontaneously combust, along with its occupants. Remember, there are three independent events required: 110V wire must wear through its insulation (and outer jacket!!); 12V wire must wear through its insulation; and it must occur in the same place and the wires must short together. Well, maybe that's 4 events. Now when events are independent the probability of all events occuring at the same time is the probability of each event multiplied together (e.g. P = Pa * Pb * Pc...) so the overall probability becomes very small very fast.

I think the odds of this happening are about 1 in a trillion, but for the sake of argument let's say someone used really crappy wire and wound the 12V wire tightly areound the 110V just to raise the odds to 1 in 100.

This means that 1 out of 100 trailers built by that person will suffer a catastrophic short during their lifetimes. Hmm, if this were a commercial effort, I would see this as a problem. For myself, building 1 trailer, I would use good wire and stop here. But, to kick the proverbial dead horse a few more times...

Let's think of some mitigations:
1) use good wire (my favorite)
2) physical separation (very good, better even than 1)
3) conduit (adds weight, but can pull new wire if you torch the old one)
4) no electricity
5) no 12V
6) no 110V
7) use gas (probably worse than the original problem)
live with the risk

Now figure the cost of each. Interestingly, 2 has no cost outside of labor. 1 adds a little cost. 3 adds weight, cost and labor but makes wire replacement easier. 4 eliminates labor and cost, while 5 and 6 reduce it. 7 is just dumb inside a confined space. 8 is what we do when we decide to accept the risk.

What else is wrong with 3? You have to drill larger holes through framing members to run that conduit, weakening the overall structure.

Now comes the part I can't help with. What is your risk aversion? If you score on the very high side of fire-phobia, you can combine several mitigations, though 3 + 4 is probably not a good combo. Make your choice and be happy with it. No one else can do that for you. Don't even let them try to persuade you. Let it be your choice, then it's only your fault if something goes wrong. I will not have you blaming me!!

One last thing - sometimes we make mistakes. That's why shuttles sometimes blow up, bridges sometimes collapse, buidlings lean. It's part of life. You cannot eliminate risk, but sometimes you can reduce it to a reasonable level. You need to decide what that level is and what you will do to get to it.

Sherman Paskett
Electrical Engineer, CISSP

[Miriam C.]

Sherman, I really don't believe the insulation will wear off, but having put a hole in every muffler I have had my concern was more a crimp in the conduit. Course I would not run conduit. I am not likely to get under and touch a live wire anyway.

Easiest mitigation is to run the 12DC along the frame and run the 120AC on the other side. Divide and conquer! That is social work for "Good God you engineers sure talk a lot."

[Taquin]

I'm not going to comment on whether you should put 12v with 120 together, but I'm going to say that if you have wires that are rubbing around enough to wear off the insulation...... You are not properly tying your wires down. There really should be little to no movement in your wires even when going down the highway. Think of all the millions of cars going down the road without wearing off their wire insulation.
Even if you put the wire in conduit, you need two things to wear off insulation. Pressure and friction/movement. And I highly doubt the weight of the wire supported by conduit has enough pressure to wear off insulation. Expecially when the conduit is in a fixed position.

Though, I own a boat at the Lake of the Ozarks and figured out that loose wires are a bad thing...

[Larwyn]

Well now Sherman. I have to say that I am not surprised that you are an Electrical Engineer because of the accuracy of your theory, but I am surprised that you are an Electrical Engineer because of your level of common sense.....

Actually, it was my "job" to give the engineers a hard time for many years, guess it's just a hard habit to break.

I too choose #1 for the Escape Pod while I choose 1 and 3 for my woodworking shop.

I'm reminded of a quote I read in an old magazine (1919) I do not remember who was credited with it but it went something like this;
"It is truly amazing how intelligent we think a person is, when he agrees with us." So in this case, at least, I think you are very smart.......

[wlooper89]

I built my trailer electrical with no training or experience, and there are some things I would like to have done differently. My education began with a book from Home Depot named something like Electrical Wiring 1-2-3. It was OK but meant for house wiring rather than trailers. I would rather have used stranded wire everywhere but there is some Romex solid wire for part of the A/C wiring where I did not expect the wires to need to bend, not thinking about vibration. I also mixed A/C and D/C wires in bundles and small raceways. In two places D/C wires run through a surface mount A/C outlet box, entering with the Romex in the same raceway and continuing to a 12V reading light.

Some of the things I did right were to have separate junction boxes for A/C and D/C wire connections; correctly sized wires, fuses and circuit breakers to protect the circuits and GFCIs to protect the happy campers.

Looking at bobhenry's dual voltage lights made me feel better. Not wanting to go back and change all the wiring I will just keep marshmallows on hand for toasting.

Bill

[caseydog]

Sherman, there is one more risk you did not cover.

Personally, I agree that the risk of wires rubbing through is not that great, but the risk of someone confusing wires is. This is especially true for those of us who are not engineers or electricians.

I can see someone deciding to alter their TD down the road (something all of us do -- some more than others). They make some changes, re-route some wires, get some wires mixed up, and zap.

I can also see someone trying to make a repair because the wife's reading light isn't working. He's at the campsite, after dark, tired, and perhaps a little cranky about having to fix this now. Zap.

I can easily imagine myself, and many non-electrician friends of mine, making either one of those mistakes.

CD

[wlooper89]

I can see someone deciding to alter their TD down the road (something all of us do -- some more than others). They make some changes, re-route some wires, get some wires mixed up, and zap.

I can also see someone trying to make a repair because the wife's reading light isn't working. He's at the campsite, after dark, tired, and perhaps a little cranky about having to fix this now. Zap.

I can easily imagine myself, and many non-electrician friends of mine, making either one of those mistakes.

CD

I am in the process of putting together a sort of owner's manual for my trailer electrical from hand written notes and diagrams. If we ever sell the trailer it might help the new owner use the trailer electrical. All of the D/C connectors are from Anderson Company. They plug together and unplug easily so I can remove components to make changes. But I have to know where to plug the connectors back together and reassemble things. I used colored electrical tape to mark each connection. Up to three different colors with the first color on each side closest to the connector. This gives enough different possibilities to make each connection unique.

For icing on the cake a Brother labeler makes nice little labels that stick on each connector saying where the wires are from or going to. Then I made a spreadsheet listing all the connections. There are columns for connector type, color, tape colors, from, to, wire sizes, wire colors and voltage. The spreadsheet was useful for adding a charging relay recently.
To be honest I never want to sell the trailer, but maybe an owner's manual will help me remember what goes where.

Bill